No problem, just train for it.
REQUIRE the dog to be steady in the yard. When you throw a mark and he is staring it down, up on his haunches, and ready to explode, mess with him. Clap your hands. Yell out. Call out different names. If he breaks, stop him (10 foot lead or e-collar). His job is to mark and to sit and wait until he is instructed to retrieve it. Whatever you use to send him, say something close.
For example, my dog's name is Hank. At least once every session I'll have him steadied either by my side or in his PLACE. I'll throw the mark and pause, letting it hit the ground and bounce around a bit. At this point every muscle in his body is tensed up, and he is ready to go.
I'll yell BOOOM
I'll yell POW
I'll whisper Henry
I'll say Bob
I'll 'command' Hammer
if he breaks, I'll stop him. He is used to this trick though, and he knows to only go on his name. So finally
I'll say Hank
And he is gone.
To to replicate scenarios in your training that the dog will encounter in the field. Having said all that, I can guarantee you that for the first two or three volleys of opening day, my shotgun will be unloaded and leaning in the corner. I will be keeping an eye on old Hank just so that he doesn't let his excitement get the best of him.
If your already hunting or don't have time to train much before hand, put the dog on a lead and attach it to the blind or a tree. Make him stay. Once a duck is shot, walk over to him, unfasten him, and send him on. He'll get the idea.
"I'll start spending less time with my dog and more with my wife when she starts fetching ducks for me"